Thermal isolation is very important for thermal based infrared devices (detector or emitters), as opposed to quantum detectors or emitters, since the detection or transmission of infrared radiation is directly related to the temperature rise achieved by the detector or emitters of the device. The better the thermal isolation of the detector or emitters the more efficient the device will be at converting radiation to heat (detector) or heat to radiation (emitter). Vacuum packaging is a very effective means to improve performance. It reduces heat flow from individual infrared units to their neighbors and/or to surrounding surfaces via ambient gas molecules by eliminating such molecules.
Because microstructure infrared detector and emitter arrays are very small and fragile, common silicon production and packaging techniques may not be suitable for large scale production of these array bearing devices. Typical infrared units in the arrays are built to be thermally isolated from the chip, as well as their neighbors, thus having elements suspended apart from the substrate to enhance the thermal isolation by having the minimal physical contacts possible. These bridges or suspension structures can be particularly fragile, therefore the method of encapsulating them into a vacuum can be critical to device yield rates.
A method for packaging the die in a batch process substantially improves the yield, reduces the cost and at the same time achieves maximum performance of these devices. This type of packaging is necessary to mass produce low cost, thermally based infrared devices. The proposed package is termed a "micropackage."
Maintaining an effective vacuum in a sealed package is often challenging due to surface outgassing. Frequently heat treatments will minimize this but such outgassing determines the effective life of the device unless it can be periodically or continuously removed. Integrating a getter into each discrete chip would be a method of maintaining a good vacuum for all chips as the getter will counteract the outgassing generated by the package surfaces.
The innovative structures taught here provide tremendous cost savings over prior designs for packaging these devices, the capability of achieving much smaller packages, as well as having the potential to greatly increase packaged device yield for lower cost.